This invention relates to the removal of lower concentrations of reactive gases from a gaseous product stream and, more particularly, to the removal of low concentrations of nitrogen oxides (hereinafter referred to as "NOx") from a nitric acid gaseous product stream.
As for example, nitric acid gaseous product streams from various production processes, both atmospheric and superatmospheric processes contained admixed NOx. When this admixed NOx falls below 0.5% it is difficult and/or expensive to remove by the known extraction processes. It is desirable both from an economical standpoint and an environmental impact standpoint to minimize this dissolved NOx. It may be desirable, however, to apply the invention disclosed herein to gases containing as much as 2.5% NOx for reasons associated with the engineering of a complete nitric acid plant.
First, the admixed NOx represents a reactive species that could be further processed to yield additional nitric acid product and thereby increase the yield of the overall process. Secondly, as NOx is toxic and potentially hazardous, the Environmental Protection Agency has set minimum standards for NOx that can be vented to the atmosphere. It is usually required that a final level of not more than about 0.015% NOx be attained. Heretofore, the low concentrations of NOx have been removed from nitric acid product streams by high pressure multiple stage absorption, catalytic combustion and catalytic reaction with ammonia. These methods have, however, proved to be either expensive or inefficient.
Accordingly, it is an object of this invention to provide an improved apparatus and process for removing low concentrations of an admixed reactive gas from a gaseous stream, which apparatus and process are both economical and efficient, and applicable to streams containing excess oxygen.
Another object of this invention is to provide an apparatus and process for physically removing low concentrations of admixed reactive gas from a gas stream and that the product removed can be further processed to yield additional nitric product.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the attached drawings.